Acousto-optic tunable filter

In combination with an automated acousto-optic tunable filter infrared analyzer system comprising:

• (a) means for directing infrared radiation through a sample species to be analyzed, which species have predetermined infrared absorption characteristics;
• (b) means for focusing the infrared radiation upon an acoustic-optic tunable filter;
• (c) an acoustic-optic tunable filter comprising an input polarizer for selectively polarizing the infrared radiation, and an optically aligned acoustic-optic crystal through which the selectively polarized infrared radiation is passed at a predetermined plane of incidence to the crystal optic axis, an acoustic transducer means coupled to a variable frequency rf power source and to the acoustic-optic crystal to launch acoustic waves in the crystal to interact with a selected narrow bandwidth portion of the polarized infrared radiation to make it distinguishable from the remaining infrared radiation, which selected narrow bandwidth portion is a function of the frequency of the rf energy and acoustic waves;
• (d) an rf energy source connected to the acoustic transducer of the acousto-optic tunable filter;
• (e) infrared radiation detection means which detects the output filtered infrared radiation from the filter and generates an output electrical signal as a function of the output filtered infrared radiation;
• (f) computing means to which the detection means output electrical signal is applied for determining the species present in the sample cell, and including means for selectively actuating the rf energy source to determine the timing and frequency of rf energy applied to the acoustic transducer mated to the acousto-optic crystal to determine the infrared wavelength selectivity or tuning of the acousto-optic tunable filter;
• the improvement wherein said acousto-optic crystal is a selected mercurous halide crystal and the plane of incidence to the crystal axis is that plane containing both the (110) and (001) axes, and wherein the acoustic waves launched into said mercurous halide crystal are in the plane of said crystal containing both the (110) and (001) axes, and wherein the infrared radiation propagates through the mercurous halide crystal at an angle equal to approximately ten degrees to the (001) crystallographic axis and wherein said acousto-optic crystal has an input face which is cut so as to be normal to the incident infrared beam which beam output is diffracted at an angle of about six degrees to the incident beam and wherein said acousto-optic crystal has an exit optical face which is cut so as to be normal to the diffracted output beam.